1. Field of the Invention
The present invention relates to patient therapy. More specifically, the present invention relates to a system, tracker, program product, and related methods to facilitate and verify proper target alignment for radiation delivery so that a treatment plan can be more accurately applied to a patient.
2. Description of the Related Art
Radiation therapy can be effective in treating certain types of cancerous tumors, lesions, or other “targets.” A vast majority of such targets can be eradicated completely if a sufficient radiation dose is delivered to the tumor or lesion volume. Complications, however, may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the target or to other healthy body organs located close to the target. The goal of various radiation procedures, such as conformal radiation therapy treatment, is to confine the delivered radiation dose to only the target volume defined by the outer surfaces of the target, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs. If the effective radiation dose is not delivered to the proper location within the patient, serious complications may result.
Radiation therapy treatment typically uses a radiation delivery apparatus or device, such as a linear accelerator or other radiation producing source, to treat the target. For example, the conventional linear accelerator includes a rotating gantry assembly which generally rotates about a horizontal axis and which has a radiation beam source or emitter positionable about the patient which can direct a radiation beam toward the target to be treated. The linear accelerator can also include a rotating treatment table assembly which generally rotates about a vertical axis and which can position the target within a rotational plane of the rotating gantry assembly. Various types of apparatus can further conform the shape of the radiation treatment beam to follow the spatial contour of the target as seen by the radiation treatment beam, from a linear accelerator, as it passes through the patient's body into the target during rotation of the radiation beam source. Multileaf collimators having multiple leaf or finger projections can be programmed to move individually into and out of the path of the radiation beam to shape the radiation beam.
Various types of radiation treatment planning systems can create a radiation treatment plan, which, when implemented, will deliver a specified dose of radiation shaped to conform to the target volume, while limiting the radiation dose delivered to sensitive surrounding healthy tissue or adjacent healthy organs or structures. Typically, the patient has the radiation therapy treatment plan prepared, based upon a diagnostic study through the use of computerized tomographic (“CT”) scanning, magnetic resonance (“MR”) imaging, or conventional simulation films, which are plain x-rays generated with the patient, and thus the patient's tumor or lesion, in the position which will be used during the radiation therapy treatment.
Placement of the radiation beams in the proper juxtaposition with the patient to be treated is typically accomplished by referencing both the radiation beam and the patient position to a coordinate system referred to as the isocenter coordinate system, which is defined by the geometry of the radiation delivery apparatus. In the linear accelerator example, the gantry, the treatment table, and collimator each have axes of rotation designed to intersect at a specific location in the middle of a treatment room, referred to as the isocenter, an origin of an interesting coordinate system of the treatment room, correspondingly referred to as the isocenter coordinate system. The isocenter coordinate system is nominally defined as horizontal (x-axis), vertical (z-axis), and co-linear with the axis of gantry rotation (y-axis). The isocenter of these three axis of interest is determined and used as a reference “point” to orient the target to the radiation treatment plan during treatment plan development and subsequent radiation delivery.
There are various methodologies of determining the location of this isocenter. For example, one methodology employs lasers directed at an apparatus having active or passive optical indicators to indicate the location of isocenter of the isocenter coordinate system to a camera or opti-electrical motion measurement system, such as, e.g., the camera system known as the Polaris®, by Northern Digital Inc., Ontario Canada. Also for example, described in co-pending application Ser. No. 11/005,643, by Scherch et al., entitled “System for Analyzing the Geometry of a Radiation Treatment Apparatus, Software and Related Methods,” incorporated by reference, is a system, apparatus, software and methods that can measure the rotation of various components of the mechanical system of the radiation treatment apparatus or device to precisely define the isocenter of the isocenter coordinate system.
Regardless of which radiation generating apparatus or technique is used at the time of the diagnostic study to develop the radiation therapy treatment plan, in the delivery of either conformal radiation therapy treatments or static radiation therapy treatments, etc., the position of the target with respect to the radiation delivery apparatus is very important. As stated above, successful radiation therapy depends on accurately placing the radiation beam in the proper position upon the target. Thus, it is necessary to relate the position of the target at the time of the diagnostic study to how the target will be positioned at the time of the radiation therapy treatment. If the position of the target is not the same as it was at the time the treatment plan was determined, the dose of radiation may not be delivered to the correct location within the patient's body. Because patients are not always positioned properly on the treatment table of the radiation therapy device, which may be a linear accelerator or a cobalt unit, for example, and because organs of a patient may move within the patient from day to day, the target may not be positioned at the exact location where the radiation therapy plan has assumed it would be located.
Various measurements and tools have been developed to help ensure proper patient positioning including the lasers, described above, and optical distance indicators (ODIs). The distance of interest for ODIs generally used in most clinical practices, is the distance from the theoretical point source of the radiation beam to the surface of the patient's skin. The point source is termed theoretical because radiation beams are typically conical but are not produced by a point source, but rather a source having a finite size. This distance from the theoretical point source to the skin surface, typically either approximately 80 cm or 100 cm in a linear accelerator, for example, is generally referred to as either target-to-surface distance (TSD) or source-to-surface distance (SSD). When the isocenter is defined, the lasers are aligned to intersect in a cross-hair pattern at the isocenter. These lasers, as well as the ODI, are used to align the patient so that the target is located at isocenter.
The ODI projects from the head of the radiation delivery apparatus to the skin surface of the patient a set of cross hairs along with a scale that indicates the distance from the theoretical point source to the skin surface marked by the crosshairs. To make the measurement, the therapist visually finds the intersection of the crosshairs and the scale and records the scale reading at the intersection point. The scale marks are typically in increments of 0.5 cm and must be visually interpolated by the therapist. Recognized by the Applicant, however, is that the slope or gradient of the patients skin, e.g., at the neck or along a breast, often makes the scale hard, if not impossible, to read. Also recognized by the Applicant is that readings can only be taken when there is unobstructed line of sight between the head of the radiation delivery apparatus and the patient's skin, making it impossible to take direct measurements of positions underneath the patient, e.g., behind the patient's neck. Further, recognized by the Applicant is that the scale frequently requires calibration, resulting in an expenditure of valuable resources. Still further, with respect to the linear accelerator example, recognized by the Applicant is that the ODI cannot be used when, for example, a multivane intensity modulated collimator (“MIMiC”) is mounted to the rotating gantry assembly.
Referencing the linear accelerator for illustrative purposes, the rotating gantry assembly and rotating treatment table assembly are heavy, slow pieces of machinery to manipulate. In order to take an ODI measurement, the patient must first be moved to directly beneath the rotating gantry head, and the rotating gantry assembly is rotated so that the ODI will shine on the selected measurement point. Additional readings would require additional movement of the treatment table assembly to reposition the patient and rotation of the gantry assembly. Recognized by the Applicant is that this process of moving the patient to directly beneath the rotating gantry head and the rotating gantry assembly so that the ODI will shine on the selected measurement point can be very time consuming. Further recognized is that for some radiation delivery procedures as many as a dozen points must be measured, each taking considerable time.
Because SSD is critical to predicting the dose delivered to the patient, and because typically a radiation treatment will deliver radiation from below the patient, it is necessary to get an accurate SSD at a measurement point where the ODI would be blocked by the rotating treatment table assembly or fixation equipment. ODI readings can only be taken where there is unobstructed line of sight between the head of the radiation delivery apparatus and the patient's skin, making it impossible to take direct measurements of positions underneath the patient, e.g., behind the patient's neck. Using the ODI to determine the SSD of visually obstructed points, the therapist takes a measurement on one side of the patient, measures the thickness of the patient with calipers typically having scales marked in increments of 0.25 cm, and then derives the SSD at the point on the opposite side of the patient. Recognized by the Applicant, however, is that there are no precise aids to ensure that the calipers are measuring points that are directly opposite each other along the central axis of the radiation beam. Recognized also is the inherent inaccuracy of having such potentially imprecise caliper scale increments.
A common procedure in the simulation room often used in conjunction with taking ODI measurements is to determine the appropriate radiation delivery path and radiation beam field size for a contoured body part, such as a patient's breast or chin. The goal of this setup is to find the appropriate location of isocenter and appropriate radiation beam field size and rotating gantry assembly angles that will result in positioning radiation beams having field edges that accurately follow a desired path. In a breast setup example, this entails determining a line tangent to the patient's chest. The tangent line is defined by marks placed by the physician on the patient's chest and side. Typically, the therapist manually constructs the setup by physically bending a solder wire along the patient's breast to capture the breast contour. Using a fluoroscopic procedure, the therapist or clinician detects the wire in live fluoroscopy images to determine the angle of the tangent line. The solder wire is in then physically moved off of the patient and onto graph paper, carefully, in order to preserve the contour, but generally without verification. The clinician then manually reconstructs the axial view of the patient contour and tangent line. From this axial view, the clinician geometrically constructs what gantry angles and radiation beam field size will produce the correct beam position. Recognized by the Applicant is that this type of contoured anatomy setup disadvantageously can take as long as 15 or 20 minutes and requires a fluoroscopy procedure which radiates the patient.
Correspondingly, recognized by the Applicant is the need for a system including tracker, program product, and related methods to facilitate and verify proper target alignment for radiation delivery that can provide an SSD for a surface of the patient having a substantial slope or gradient, that does not require individual calibration, and that can be used whether or not a MIMiC is mounted to the rotating gantry assembly of a linear accelerator when such radiation delivery apparatus is used. Also recognized is the need for a system that can quickly and efficiently deliver an SSD measurement for each of multiple surfaces of the patient without requiring repositioning of the patient in order to take each individual reading. Further, is the need for a system that can deliver actual SSD measurements for surfaces of the patient obstructed by various structures including the rotating table assembly of the linear accelerator when such radiation delivery apparatus is used. Still further, recognized is the need for a system that can provide accurate SSD and patient thickness measurements for measurement points opposite each other along the central axis of the radiation extending through the isocenter of the radiation delivery apparatus. Additionally, recognized is the need for a system that can accurately provide measurement data for a contoured portion of the patient's anatomy and that can help determine required radiation beam angles, beam field size, and location of the edges of the beam field.